Methods for operating gas turbine engines

ABSTRACT

A method for operating a pulse detonation system. The method includes providing a pulse detonation chamber including a plurality of detonation tubes extending therein, and detonating a mixture of fuel and air within each detonation tube such that at least a first tube is detonated at a different time than at least a second detonation tube.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/929,910, filed Aug. 30, 2004, now U.S. Pat. No. 7,007,455 whichclaims priority to U.S. Pat. No. 6,813,878, issued Nov. 9, 2004, both ofwhich are hereby incorporated by reference and are assigned to assigneeof the present invention.

BACKGROUND OF THE INVENTION

This invention relates generally to gas turbine engines and moreparticularly, to a pulse detonation system for a gas turbine engine.

At least some known pulse detonation systems use a series of repetitivedetonations within a detonation chamber to produce a high pressureexhaust. More specifically, a fuel and air mixture is periodicallydetonated within a plurality of tubes within the detonation chamber tocreate hot combustion gases which cause pressure waves to propagate atsupersonic speeds within the tubes and chamber. The pressure wavescompress the hot combustion gases, which increases a pressure, density,and a temperature of the gases to produce thrust as the pressure wavespass the exit of an open end of the detonation chamber.

Gas turbine engines producing thrust using pulse detonation systemstypically have a higher thrust to weight ratio because they aregenerally smaller and weigh less than conventional gas turbine engines.In addition, pulse detonation engines may include fewer rotating parts,produce lower emissions, and be more fuel efficient than conventionalgas turbine engines. Pulse detonation engines also may not suffer stalland startup problems that may be experienced by some known gas turbineengines because of separation in and around compressor blades within theconventional engines.

However, pressures generated within the detonation chamber of some knownpulse detonation systems may cause at least some known pulse detonationengines to be very loud and may facilitate structural failures withinthe engines. More specifically, each detonation tube has a firingfrequency that is dependent upon the dynamics of detonation and ageometry of the tube. While conventional detonation chambers createthrust by imparting overall pressure rise the hot combustion gases,known pulse detonation tubes also have a dynamically varying positivepressure rise and fall in each tube as each tube repeatedly fires. Thedynamic periodicity of such pressures may induce dynamic pressure loadsto the pulse detonation system which may propagate from the system asacoustic pressure waves, i.e., noise.

BRIEF SUMMARY OF THE INVENTION

In one aspect, a method is provided for operating a pulse detonationsystem. The method includes providing a pulse detonation chamberincluding a plurality of detonation tubes extending therein, anddetonating a mixture of fuel and air within each detonation tube suchthat at least a first tube is detonated at a different time than atleast a second detonation tube.

In another aspect, a control system is provided for a pulse detonationsystem including a plurality of detonation tubes. The control systemincludes a processor that is programmed to control detonation of amixture of fuel and air within each detonation tube, such that at leasta first detonation tube is detonated at a time that is different from atime of detonation of at least a second detonation tube.

In yet another aspect, a pulse detonator is provided for a pulsedetonation system. The chamber includes an inner casing, and an outercasing that is substantially coaxial with the inner casing, and isspaced radially outwardly from the inner casing. The inner and outercasings define a detonation chamber therebetween. A plurality ofdetonation tubes extend at least partially within the detonationchamber. At least a portion of at least a first detonation tube isstacked radially outwardly from at least a portion of at least anadjacent second detonation tube, such that a first central axis of thefirst detonation tube is spaced radially outwardly from a second centralaxis of the adjacent second detonation tube.

In even another aspect, a pulse detonation system is provided thatincludes a pulse detonator including a plurality of detonation tubesextending at least partially within the pulse detonator, and a controlsystem that includes a processor programmed to control the detonation ofa mixture of fuel and air within each detonation tube such that at leasta first detonation tube is detonated at a time that is different from atime of detonation of at least a second detonation tube.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an exemplary gas turbine engine;

FIG. 2 is a schematic illustration of an exemplary pulse detonationsystem for use with the gas turbine engine shown in FIG. 1; and

FIG. 3 is a cross-sectional view of a portion of a detonator shown inFIG. 2 and taken alone line 3—3.

DETAILED DESCRIPTION OF THE INVENTION

The term computer, as used herein, means any microprocessor-based systemincluding systems using microcontrollers, reduced instruction setcircuits (RISC), application specific integrated circuits (ASICs), logiccircuits, and any other circuit or processor capable of executing thefunctions described herein.

FIG. 1 is a schematic illustration of a gas turbine engine 10 includinga low pressure compressor 12, a high pressure compressor 14, and a pulsedetonation system 16. Engine 10 also includes a high pressure turbine18, and a low pressure turbine 20. Compressor 12 and turbine 20 arecoupled by a first shaft 24, and compressor 14 and turbine 18 arecoupled by a second shaft 26. In one embodiment, engine 10 is a F110/129engine available from General Electric Aircraft Engines, Cincinnati,Ohio.

In operation, air flows through low pressure compressor 12 from an inletside 28 of engine 10 and compressed air is supplied from low pressurecompressor 12 to high pressure compressor 14. Compressed air is thendelivered to pulse detonation system 16 where it is mixed with fuel andignited. The combustion gases are channeled from pulse detonation system16 to drive turbines 18 and 20 and provide thrust from an outlet 30 ofengine 10.

FIG. 2 is a schematic illustration of an exemplary pulse detonationsystem 50 for use with a gas turbine engine, for example engine 10(shown in FIG. 1). FIG. 3 is a cross-sectional view of a portion of apulse detonator 52 for pulse detonation system 50 taken along line 3—3.Pulse detonation system 50 includes a pulse detonator 52 and a controlsystem 53. Pulse detonator 52 includes annular outer and inner casings54 and 56, respectively, and a plurality of detonation tubes 58. Outerand inner casings 54 and 56 are disposed substantially coaxially about alongitudinal centerline axis 60 of pulse detonation system 50 and arespaced radially apart such that a detonation chamber 62 is definedtherebetween. Pulse detonator 52 includes an inlet end 64, an outlet end66, and detonation tubes 58. Detonation tubes 58 extend throughdetonation chamber 62 along axis 60, and also extend a length 68measured from an upstream end 70 that is adjacent chamber inlet side 64,to a downstream end 72. An exhaust chamber 73 is defined betweendetonation tube downstream ends 72 and detonator outlet end 66. Exhaustchamber 73 includes an upstream end 74 and a downstream end 75.

Detonation tubes 58 are stacked in an array 76 within detonation chamber62 such that a plurality of tubes 58 are spaced circumferentially aroundaxis 60, and such that a plurality of tubes 58, or a portion of aplurality of tubes 58, are stacked radially outwardly from inner casing56 to outer casing 54. In an alternative embodiment, detonation tubes 58are stacked within detonation chamber 62 such that a plurality of tubes58 are spaced circumferentially around axis 60 and such that only onetube 58 is positioned radially between inner casing 56 and outer casing54.

In the exemplary embodiment, detonation tubes 58 each have asubstantially circular cross-sectional geometric shape, and tubes 58substantially occupy the space defined between inner and outer casings56 and 54, respectively. Furthermore, as illustrated in FIG. 3, tubes 58are arranged in stacks 78 which include smaller diameter tubes 58, andstacks 80 which include larger diameter tubes 58. More specifically, inthe exemplary embodiment, a central axis 81 of a first tube 58 is spacedradially outwardly from a central axis 83 of a second tube 58 that isadjacent the first tube 58. However, it will be understood that thenumber, geometric shape, configuration, and/or diameter of tubes 58 willvary depending upon the particular application, and as described below.For example, in one embodiment, detonation tubes 58 each haveapproximately equal diameters. In another embodiment, detonation tubes58 include tubes of varying diameter. Furthermore, it will be understoodthat a length 68 of each tube 58 will vary depending upon the particularapplication, and as described below. For example, in one embodiment,detonation tubes 58 each include approximately equal lengths 68. Inanother embodiment, detonation tubes 58 include tubes of varying length68. The examples herein described are intended as exemplary only, andare not intended to limit the number, geometric shape, configuration,diameter, and/or length 68 of detonation tubes 58.

Control system 53 includes a computer and/or processor 82, a pluralityof pressure feedback sensors 84, and a firing system 86 that is coupledto detonation tubes 58 adjacent upstream ends 70. As described below,firing system 86 charges each tube 58 with compressed air and fuel, andperiodically detonates the mixture of fuel and air within each tube 58to produce hot combustion gases within each tube 58 and exhaust chamber73. Sensors 84 are coupled to outer casing 54 adjacent exhaust chamber73, and measure a pressure of combustion gases within exhaust chamber73. Computer 82 is electrically coupled to sensors 84 and firing system86. In one embodiment, computer 82 is a multiple-input, multiple-output,(MIMO) electronic control computer. In an alternative embodiment,control system 52 includes only one pressure feedback sensor 84.

Firing system 86 charges each detonation tube 58 with fuel, from a fuelsource (not shown), and compressed air from compressors 12 and 14 (shownin FIG. 1). The mixture is detonated to produce hot combustion gaseswithin each tube 58 that flow downstream through exhaust chamber 73 andare discharged from detonation chamber outlet end 66 towards turbines 18and 20 (shown in FIG. 1) and engine outlet 30 (shown in FIG. 1). In oneembodiment, compressed air and fuel are mixed by firing system 86 beforethe mixture is supplied to each detonation tube 58. In an alternativeembodiment, compressed air and fuel are each independently supplied toeach detonation tube 58 and are mixed within each detonation tube 58.

Firing system 86 does not continuously detonate the mixture within tubes58. Rather, and as described below, firing system 86 periodically cyclesthe detonation of the fuel/air mixture to generate pressure waves, orpulses, that propagate through the combustion gases to facilitateincreasing the pressure and temperature of the combustion gases toprovide thrust. The pressure waves propagate downstream through tubes 58and exhaust chamber 73.

The methods and systems described herein facilitate containing largerdynamic pressure variations within tubes 58 and exhaust chamber upstreamend 74, such that dynamic pressure variations are reduced within exhaustchamber downstream end 75 as combustion gases exit engine exhaust 30.More specifically, firing system 86 detonates the fuel air mixture ineach tube 58, referred to herein as filing each tube 58, sequentiallysuch that only a desired number of tubes 58 are fired simultaneously. Inone embodiment, each tube 58 is fired independently at a different time.In an alternative embodiment, a plurality of tubes 58 are firedsimultaneously, and a plurality of tubes 58 are firednon-simultaneously.

As each individual tube 58 fires, a positive-going pressure pulse isemitted that propagates downstream through exhaust chamber 73 fromupstream end 74 to downstream end 75. Sensors 84 sense the pressurepulses from various tubes 58 within exhaust chamber 73. Computer 82,using an active noise-control algorithm, determines an appropriatefiring sequence for tubes 58, based on the sensed pressure pulses, suchthat dynamic pressure variations are reduced within exhaust chamber 73,while a high and steady pressure of combustion gases is exhaustedthrough detonator outlet end 66 and ultimately, engine exhaust 30. Morespecifically, computer 82 controls firing of each tube 58 within array76 such that low, positive pressure regions of pressure pulses aresubstantially aligned with high, positive pressure regions of adjacentpulses. Aligning adjacent pulses in such a manner facilitates reducingpressure variations. Specifically, as pressure pulses propagate throughexhaust chamber 73, higher amplitude dynamic pressure variations aresubstantially smoothed out, causing the exhaust of combustion gasesexiting exhaust chamber 73 and engine exhaust 30 to be at asubstantially uniform and high pressure. Accordingly, high amplitudedynamic pressure variations are substantially contained within tubes 58and exhaust chamber upstream end 74, such that a reduction in dynamicpressure loads is induced within system 50, and the number and intensityof acoustic pressure waves emitted by system 50 are facilitated to bereduced. As a result, structural failures associated with system 50 anda level of noise emitted by system 50 are facilitated to be reduced.

In one embodiment, each tube 58 within array 76 is fired such that highpositive pressure regions of pressure pulses align with high positiveregions of adjacent pressure pulses to facilitate increasing thepositive pressure of the pressure pulses, and thereby increasing thepressure of the hot combustion gases exhaust from exhaust chamber 73.

An exhaust chamber length 88, measured between the downstream end 72 ofthe longest tube 58 within array 76 and detonator outlet end 66, isvariably selected to facilitate reducing dynamic pressures to apre-determined level. More specifically, the geometry and configurationof detonation tubes 58 is also variably selected. For, example, in oneembodiment, a greater number of smaller diameter tubes 58 may facilitatea shorter exhaust chamber length 88, than a smaller number of largerdiameter tubes 58.

The above-described pulse detonation system facilitates reducingstructural failures of the system and noise produced by the system. Morespecifically, by aligning low positive pressure regions with highpositive pressure regions of adjacent pulses, the system facilitatesreducing dynamic pressure loads within the system and facilitatesreducing the number and intensity of acoustic pressure waves emitted bythe system. In addition, the above-described pulse detonation system mayfacilitate increasing the thrust of a pulse detonation engine byaligning high positive pressure regions with high positive regions ofadjacent pressure pulses. As a result, a pulse detonation system isprovided which may facilitate an engine that has a longer engine life,and operates with increased thrust, increased efficiency, and reducednoise.

Exemplary embodiments of pulse detonation systems are described above indetail. The systems are not limited to the specific embodimentsdescribed herein, but rather, components of each system may be utilizedindependently and separately from other components described herein.Each pulse detonation system component can also be used in combinationwith other pulse detonation system components.

While the invention has been described in terms of various specificembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theclaims.

1. A method for operating a pulse detonation system, said methodcomprising: providing a pulse detonation chamber including a pluralityof detonation tubes extending therein, wherein at least one detonationtube has a length that is unequal to a length of at least one otherdetonation tube; and detonating a mixture of fuel and air within eachdetonation tube such that at least a first detonation tube is detonatedat a different time than at least a second detonation tube.
 2. A methodin accordance with claim 1 wherein detonating a mixture of fuel and airwithin each detonation tube comprises detonating at least two detonationtubes such that a region of a first pressure wave generated issubstantially aligned with a region of a second pressure wave generated.3. A method in accordance with claim 1 wherein providing a pulsedetonation chamber comprises providing a pulse detonation chamberincluding at least one detonation tube that has a diameter that isunequal to a diameter of at least one other detonation tube.
 4. A methodin accordance with claim 1 wherein providing a pulse detonation chambercomprises: providing a pulse detonator including an inner casing, and anouter casing that is substantially coaxial with the inner casing and isspaced radially outwardly from the inner casing such that a pulsedetonation chamber is defined between the inner and outer casings; andstacking at least a portion of at least one first detonation tuberadially outwardly from at least a portion of at least one adjacentdetonation tube within the detonation chamber such that a first centralaxis of the first detonation tube is spaced radially outwardly from asecond central axis of the adjacent detonation tube.